1. Field of the Invention
The present invention relates to radio telephone apparatuses such as car telephones and methods of controlling them and, more particularly, to a radio telephone apparatus and the method of controlling it wherein the operation in which a power source switch is turned OFF by an erroneous operation in a talk mode is inhibited.
2. Description of the Related Art
A prior art radio telephone apparatus, for example, a car telephone comprises a transceiver unit and a control unit. The transceiver unit includes a power supply circuit for receiving power from a battery to generate necessary power source voltages, a controller, a radio circuit, an audio circuit, and a power source line switch provided between the battery and the power source part. The control unit includes a key pad through which a dial number or the like is input, a controller, a handset receiver, a handset transmitter, a loudspeaker for generation of a ringing tone, and a power source key input detecting circuit. The control unit is coupled to a party telephone set (an ordinary home telephone set or another car telephone) through an antenna, a radio circuit and a base station to form a talk path between the control unit and the party telephone set, so that a speech can be realized through the handset receiver and transmitter.
With the above arrangement, the power source switch for turning ON the power supply of the apparatus is separately provided from the key pad, but recently the power source switch is often arranged to be one key of the key pad. In the latter case, a certain key of the key pad is used as the power source switch so that continuous depression of this key for a predetermined period of time causes the power source key input detecting circuit to detect the depressed state of the key, whereby the power source line switch in the transceiver unit is turned ON. A second continuous depression of the key for the predetermined period of time causes the power source key input detecting circuit to detect the second depressed state of the key, whereby the power source line switch is turned OFF. In other words, each time the key, to which the power source switch function is allocated, is continuously depressed (turned ON) for the predetermined time, the power source line switch is alternately changed over from its ON state to its OFF state and vice versa.
Meanwhile, since the control unit is arranged to have the handset integrally built therein, the user must talk with the party holding the control unit in his or her hand in a talk mode. For this reason, the prior art apparatus has a problem in that it is possible for the user to erroneously touch the key allocated as the power source switch during the conversation with the other party, which undesirably results in the apparatus power supply being turned OFF and thus the speech path would be cut off.
Like the power source switch, a mute switch for interrupting a transmission voice at the call sender side to prevent the party from listening to the voice in the talk mode, a volume switch and other such switches are embodied respectively in the form of one key of the key pad.
In this way, in the case where keys of the key pad are arranged to be used as the power source switch, as the mute switch and as the volume switch, the controller in the transceiver unit periodically examines the ON or OFF state of each of the keys of the key pad and compares or collates the examined state with the previous ON or OFF state to determine which key has been operated. For example, if one of the keys having a mute function allocated thereto is operated, then the controller which controls the transmission talk muting switch is placed in its OFF state, thus cutting or deadening a transmission talk voice.
Meanwhile, it is common that about 6-9 function keys including the mute switch key are provided in a car telephone. With such an arrangement one function is allocated to one of the function keys of the key pad as mentioned above. However, when it is necessary to increase the number of function keys for the system to accommodate more functions, the physical size of the key pad must be disadvantageously restricted, as well as the number of allowable additional function keys, thus resulting in a system that cannot cope with the increase in the number of function keys. One of the measures taken to solve this problem is to enlarge the size of the key pad. However, this measure disadvantageously involves the increased size of the control unit containing the key pad.